Occasionally lightening strikes the vent lines on oil field atmospheric condensate storage tanks and, because flammable vapors are being vented from the tanks, ignition may occur and the ensuing flame and fire can result in the loss of considerable product and equipment. Typically, such atmospheric condensate storage tanks are located in isolated areas and are not supervised by operating personnel. It is important, therefore, to provide automatic closure of the vent so that the flame will be quickly snuffed.
As a result of a patentability search conducted for the present invention, the following prior art approaches were uncovered:
______________________________________ INVENTOR U.S. PAT. NO. DATE ISSUED ______________________________________ C. A. King 471,615 Mar. 29, 1892 W. M. Bowles 1,162,019 Nov. 30, 1915 W. M. Bowles 1,238,983 Sept. 4, 1917 W. M. Bowles 1,265,877 May 14, 1918 W. M. Bowles 1,298,872 Apr. 1, 1919 V. M. Henrietta 1,573,938 Feb. 23, 1926 G. C. Schmidt 1,672,042 June 5, 1928 S. H. Brooks 1,803,460 May 5, 1931 A. W. Wheaton 1,918,728 July 18, 1933 J. R. Williams 2,913,320 Nov. 17, 1959 Clarence Williams 3,613,942 Oct. 19, 1971 ______________________________________
The 1892 patent to King teaches the use of a fusible link which in the presence of fire will melt causing two valves to close thereby sealing off a glass liquid fuel level indicator. The melting of the fusible link causes a counterweight to act on a connecting rod to close the upper and lower valves. Thus, in the event of a fire in or near the tank, any rupturing of the glass liquid level gauge, which would spill fuel from the storage tank, is quickly closed under the teachings of the King invention.
The four patents to Bowles are all directed to safety vents for oil storage tanks and are generally constructed using weighted valves and fusible links to automatically close a valve located in the vent in case of fire. In U.S. Pat. No. 1,162,019, Bowles utilizes a fuse wire located in the vent for holding open a weighted valve. In the event of a fire in the vent, the fuse wire melts releasing the weighted valve to close over the vent. In U.S. Pat. Nos. 1,238,983 and 1,265,877, the aforesaid structure is modified by placing the fuse wire just beyond the outlet of the vent and by providing an alarm device. In U.S. Pat. No. 1,298,872, rather than using a fusible wire, Bowles utilizes a fusible link. The Bowles '872 patent also provides a hood over the vent to concentrate heat from the flame on the fusible element to more quickly close the valve.
In the 1933 patent to Wheaton (U.S. Pat. No. 1,918,728), a fusible link is utilized on the exterior of the tank and vent. Upon release due to a fire, a counterweighted lever releases an internal valve to close over the vent. A separate manual valve on the vent pipe is disclosed for also manually closing off the vent.
The 1925 patent issued to Henrietta et al (U.S. Pat. No. 1,573,938) utilizes a plurality of fusible elements located external of the tank and vent to close a valve located near the end of the vent.
The 1928 patent issued to Schmidt et al (U.S. Pat. No. 1,672,042) teaches the use of a manually actuated flame snuffer for a tank vent. A spring holds open a valve in normal operation and, in the event of fire, a chain is pulled closing the valve and snuffing the flame. When the fire is snuffed out, the chain is released and the spring biases the valve back into its normally open position.
The remaining patents uncovered in the search are believed not to be as pertinent to the present invention as those set forth and discussed above.
Of all of the above patents, only the four Bowles patents, the Henrietta et al and Schmidt et al patents are believed to be pertinent to the teachings of the present invention. The Bowles patents teach the use of a fused element directly in the outlet path of the vent. The Henrietta et al patent teaches the use of the safety valve being located near the end of the vent and the Schmidt et al patent teaches the use of a manual snuffer in case of a fire. However, none of these approaches suggest either individually or in combination with each other an approach involving a combined automatic and manual fire snuffer for closing the end of a tank vent line.